Japanese Patent Application No. 2001-121583 filed on Apr. 19, 2001, is hereby incorporated by reference in its entirety.
The present invention relates to a central blood pressure waveform estimation device and a peripheral blood pressure waveform detection device.
A central blood pressure, specifically, a blood pressure and a blood pressure waveform in the origin of the aorta can be important information for treatment policy planning, post-operative or post-treatment management, intensity management in ergotherapy, and the like for patients suffering from a heart disease. However, it is difficult to non-invasively measure the central blood pressure. In particular, it is very difficult to measure the central blood pressure when the patient takes exercise or the like. Because of this, the central blood pressure and the blood pressure waveform are not generally utilized in clinical applications.
The blood pressure waveform in the peripheral vessel is considered to be the central blood pressure waveform changed by transmission characteristics of a tube through which the pressure wave is transmitted. Based on this idea, it is known in the art that the central blood pressure waveform can be derived from the pressure pulse waveform in the peripheral artery with high precision using a transfer function measured in advance between the blood pressure waveform in the origin of the aorta and the blood pressure waveform in the peripheral artery such as the brachial artery or the radial artery, specifically, the pressure pulse waveform.
It is also known in the art that the pressure pulse wave in the peripheral artery such as the radial artery can be non-invasively detected with high precision using applanation tonometry which measures the pressure using a pressure sensor pressed against the artery so that part of the blood vessel wall is flattened.
Details of these studies are described in McDonald""s Blood Flow in Arteriesxe2x80x94Theoretical, Experimental and Clinical Principles (Fourth Edition), Chapter 22, by W. W. Nichols and M. F. O""Rourke.
However, it is necessary to measure the pulse wave while allowing the person being measured to be in a resting state in order to stably detect the pulse wave in the peripheral artery such as the radial artery using applanation tonometry or the like.
Moreover, since only one transfer function is used to derive the blood pressure waveform in the aorta from the pulse wave in the peripheral artery regardless of the age and state of the subject, it may be difficult to maintain precision of the blood pressure waveform in the aorta to be derived.
The present invention has been achieved in view of the above-described problems. The present invention may provide a central blood pressure waveform estimation device exhibiting at least one of the following effects.
(1) A central blood pressure waveform can be derived by using a waveform of a peripheral pulse wave which is non-invasively detected.
(2) A pulse wave in a peripheral artery can be stably detected without forcing a subject to be in a resting state.
(3) A central blood pressure waveform can be derived from a pulse wave in a peripheral artery with high precision regardless of an age or state of an subject.
A central blood pressure waveform estimation device according to a first aspect of the present invention comprises:
a pulse wave detection section which non-invasively detects a peripheral pulse wave;
a transfer function storage section which stores a transfer function calculated in advance based on a waveform of the peripheral pulse wave detected by the pulse wave detection section and a central blood pressure waveform corresponding to the peripheral pulse waveform; and
a central blood pressure waveform calculation section which calculates a central blood pressure waveform corresponding to a waveform of a peripheral pulse wave newly detected by the pulse wave detection section, based on the newly-detected peripheral pulse waveform and the transfer function.
According to the first aspect of the present invention, a central blood pressure waveform, specifically, a blood pressure waveform in an origin of an aorta can be derived from a peripheral pulse waveform which is non-invasively detected.
A central blood pressure waveform estimation device according to a second aspect of the present invention comprises:
a pulse wave detection section which non-invasively detects a peripheral pulse wave;
a transfer function storage section which stores a transfer function calculated in advance based on a waveform of the peripheral pulse wave detected previously and a central blood pressure waveform corresponding to the peripheral pulse waveform; and
a central blood pressure waveform calculation section which calculates a central blood pressure waveform corresponding to a waveform of a peripheral pulse wave newly detected by the pulse wave detection section, based on the newly-detected peripheral pulse waveform and the transfer function.
xe2x80x9cA waveform of the peripheral pulse wave detected previouslyxe2x80x9d is a waveform of a peripheral pulse wave detected by a device for pulse wave detection formed in the same manner as the above pulse wave detection section, for example.
According to the second aspect of the present invention, a blood pressure waveform in an aorta can be derived from a peripheral pulse waveform which is non-invasively detected.
Moreover, since a transfer function calculated in advance based on a waveform of a peripheral pulse wave detected by a device for pulse wave detection formed in the same manner as the pulse wave detection section of the central blood pressure waveform estimation device is stored in the transfer function storage section, it is unnecessary to calculate a transfer function for each central blood pressure waveform estimation device.
A central blood pressure waveform estimation device according to a third aspect of the present invention comprises:
a pulse wave detection section which non-invasively detects a peripheral pulse wave;
a blood pressure measurement section which measures a blood pressure in an area near a portion in which a peripheral pulse wave is detected by the pulse wave detection section;
a conversion section which converts a waveform of the peripheral pulse wave detected by the pulse wave detection section into a peripheral blood pressure waveform using a value of the blood pressure measured by the blood pressure measurement section;
a transfer function storage section which stores a transfer function calculated in advance based on the peripheral blood pressure waveform obtained by the conversion section and a central blood pressure waveform corresponding to the peripheral blood pressure waveform; and
a central blood pressure waveform calculation section which calculates a central blood pressure waveform corresponding to a peripheral blood pressure waveform obtained by converting a waveform of a pulse wave newly detected by the pulse wave detection section using the conversion section, based on this peripheral blood pressure waveform and the transfer function.
According to the third aspect of the present invention, a blood pressure waveform in an aorta can be derived from a peripheral blood pressure waveform obtained by converting a waveform of a peripheral pulse wave which is non-invasively detected.
A central blood pressure waveform estimation device according to a fourth aspect of the present invention comprises:
a pulse wave detection section which non-invasively detects a peripheral pulse wave;
a blood pressure value storage section which stores a value of a blood pressure measured previously in an area near a portion in which a peripheral pulse wave is detected by the pulse wave detection section;
a conversion section which converts a waveform of the peripheral pulse wave detected by the pulse wave detection section into a peripheral blood pressure waveform using the blood pressure value stored in the blood pressure value storage section;
a transfer function storage section which stores a transfer function calculated in advance based on the peripheral blood pressure waveform obtained by the conversion section and a central blood pressure waveform corresponding to the peripheral blood pressure waveform; and
a central blood pressure waveform calculation section which calculates a central blood pressure waveform corresponding to a peripheral blood pressure waveform obtained by converting a waveform of a pulse wave newly detected by the pulse wave detection section using the conversion section, based on the peripheral blood pressure waveform and the transfer function.
According to the fourth aspect of the present invention, a blood pressure waveform in an aorta can be derived from a waveform of a peripheral pulse wave which is non-invasively detected using the blood pressure value storage section in place of the blood pressure measurement section according to the third aspect of the invention.
Each of the central blood pressure waveform estimation devices according to the first to fourth aspects of the present invention may further comprise a central blood pressure waveform index derivation section which derives an index from a central blood pressure waveform calculated by the central blood pressure waveform calculation section.
The index derived by the central blood pressure waveform index derivation section may be a pre-systolic blood pressure.
The index derived by the central blood pressure waveform index derivation section maybe a post-systolic blood pressure.
The index derived by the central blood pressure waveform index derivation section may be a diastolic blood pressure.
The index derived by the central blood pressure waveform index derivation section may be a differential pressure between a post-systolic blood pressure and a blood pressure at a dicrotic notch.
The index derived by the central blood pressure waveform index derivation section may be a ratio of a post-systolic blood pressure to a blood pressure at the peak of a tidal wave.
The central blood pressure waveform estimation device having the central blood pressure waveform index derivation section may further comprise:
a central blood pressure waveform index storage section which stores the index of a central blood pressure waveform; and
a change analysis section which analyzes the change in the index of a central blood pressure waveform, based on an index newly derived by the central blood pressure waveform index derivation section and the index of the central blood pressure waveform stored in the central blood pressure waveform index storage section.
The change analysis section may include:
a basal central blood pressure waveform index derivation section which derives an index of a basal central blood pressure waveform, which is an index of a central blood pressure waveform when basal metabolism of a subject is in the lowest region in a predetermined period of time, from the index of the central blood pressure waveform stored in the central blood pressure waveform index storage section; and
a basal central blood pressure waveform index storage section which stores the basal central blood pressure waveform index derived by the basal central blood pressure waveform index derivation section,
wherein the change in the index of a central blood pressure waveform may be analyzed, based on the index of the central blood pressure waveform derived by the central blood pressure waveform index derivation section and the basal central blood pressure waveform index stored in the basal central blood pressure waveform index storage section.
The central blood pressure waveform estimation device having the central blood pressure waveform index derivation section may further comprise:
a data input section to which an actual age of a subject is input; and
a comparative analysis section which compares and analyzes an index of a central blood pressure waveform, based on the index of the central blood pressure waveform derived by the central blood pressure waveform index derivation section and a standard index of a central blood pressure waveform at the actual age.
In each of the central blood pressure waveform estimation devices according to the first to fourth aspects of the present invention, the pulse wave detection section may be formed to detect a plethysmogram which changes corresponding to the blood flow, as the change in the amount of erythrocytes in capillary vessels near the skin.
This enables a pulse wave in a peripheral artery to be stably detected without forcing a subject to be in a resting state.
The plethysmogram which changes corresponding to the blood flow can be detected as the change in the amount of erythrocytes in capillary vessels near the skin. Since the change can be detected as a change in the amount of transmission or reflection of light irradiated onto the skin, it is not necessary to place a sensor at a position of a peripheral artery such as a radial artery. Because of this, the pulse wave detection section can stably detect the change in the amount of erythrocytes in capillary blood vessels near the skin as a pulse wave in the peripheral artery (plethysmogram).
In each of the central blood pressure waveform estimation devices according to the first to fourth aspects of the present invention, the transfer function storage section may store a plurality of transfer functions corresponding to a plurality of different states of a single subject such as states in which at least one of a cardiac function state and an arterial state differs. The transfer function is not constant for a single subject. The transfer function is changed depending upon the cardiac function state, arterial state, psychological tension state, psychological relaxation state, or the like. Since the state of an subject whose central blood pressure waveform is estimated by measuring the pulse wave varies at the time of measurement, the transfer functions are stored corresponding to various states. In this case, the central blood pressure waveform calculation section may calculate a central blood pressure waveform by selecting one transfer function corresponding to the pulse rate derived from the pulse wave, for example, from among a plurality of transfer functions based on information detected by the pulse wave detection section.
This enables a central blood pressure waveform to be derived from a pulse wave in a peripheral artery with high precision regardless of a state of a subject.
In each of the central blood pressure waveform estimation devices according to the first to fourth aspects of the present invention, the transfer function storage section may store a plurality of transfer functions corresponding to different ages; and the central blood pressure waveform calculation section may calculate a central blood pressure waveform by selecting a transfer function corresponding to the age of a subject whose pulse wave is detected by the pulse wave detection section, from the plurality of transfer functions.
This enables a central blood pressure waveform to be derived from a pulse wave in a peripheral artery with high precision regardless of the age of a subject.
In each of the central blood pressure waveform estimation devices according to the first to fourth aspects of the present invention, the transfer function storage section may store a plurality of transfer functions corresponding to different physiological ages; and the central blood pressure waveform calculation section may calculate a central blood pressure waveform by selecting a transfer function corresponding to the physiological age of a subject whose pulse wave is detected by the pulse wave detection section from the plurality of transfer functions.
This enables a central blood pressure waveform to be derived from a pulse wave in a peripheral artery with high precision regardless of the physiological age of a subject.
In the central blood pressure waveform estimation device according to the fourth aspect of the present invention, the blood pressure value storage section may store a plurality of blood pressure values corresponding to a plurality of different states of a single subject such as states in which at least one of the cardiac function state and the arterial state differs. In this case, the conversion section may read a blood pressure value selected from the plurality of blood pressure values stored in the blood pressure value storage section, based on information from the pulse wave detection section.
The blood pressure value is not constant for a single subject. The blood pressure value is changed depending upon the cardiac function state, arterial state, psychological tension state, psychological relaxation state, or the like. Since a state of a subject whose central blood pressure waveform is estimated by measuring the pulse wave varies at the time of measurement, the blood pressure values are stored corresponding to various states. Since these various states correlate with heart rate (or pulse rate) or an index which indicates the characteristics of the pulse waveform, the blood pressure values in various states may be connected with heart rate or the above index and stored. In this case, the conversion section may calculate heart rate or the above index or the like based on the information from the pulse wave detection section, and read the blood pressure value selected from a plurality of blood pressure values based on the heart rate or the above index or the like.
Alternatively, states of a subject at the time of measurement may be input. As a state of a subject which may vary the blood pressure value, there are states after a meal, bath, exercise and the like, being different from the resting period, or a psychological tension state or a psychological relaxation state. In addition to the blood pressure value during the resting period, a plurality of blood pressure values corresponding to the above-described states may be stored in the blood pressure value storage section. The conversion section may read a blood pressure value selected from the plurality of blood pressure values based on information from a data input section.
A peripheral blood pressure waveform detection device according to a fifth aspect of the present invention comprises:
a pulse wave detection section which non-invasively detects a peripheral pulse wave;
a blood pressure measurement section which measures a blood pressure in an area near a portion in which a peripheral pulse wave is detected by the pulse wave detection section; and
a conversion section which converts a waveform of the peripheral pulse wave detected by the pulse wave detection section into a peripheral blood pressure waveform using a value of the blood pressure measured by the blood pressure measurement section.
A peripheral blood pressure waveform detection device according to a sixth aspect of the present invention comprises:
a pulse wave detection section which non-invasively detects a peripheral pulse wave;
a blood pressure value storage section which stores a value of a blood pressure measured previously in an area near a portion in which a peripheral pulse wave is detected by the pulse wave detection section; and
a conversion section which converts a waveform of the peripheral pulse wave detected by the pulse wave detection section into a peripheral blood pressure waveform using the blood pressure value stored in the blood pressure value storage section.
In each of the peripheral blood pressure waveform detection devices according to the fifth and sixth aspects of the present invention, the pulse wave detected by the pulse wave detection section may be a plethysmogram which changes corresponding to the blood flow.
In the peripheral blood pressure waveform detection device according to the sixth embodiment of the present invention, the blood pressure value storage section may store a plurality of blood pressure values corresponding to a plurality of different states of a single subject such as a state in which at least one of the cardiac function state and the arterial state differs.